Impact of Air Pollution on the Ocular Surface and Tear Cytokine Levels: A Multicenter Prospective Cohort Study

PURPOSE: To assess air pollution-induced changes on ocular surface and tear cytokine levels. METHODS: As a prospective multicenter cohort study, 387 dry eye disease (DED) participants were recruited from five provinces in China and underwent measurements of ocular surface disease index (OSDI), Schirmer’s I test (ST), tear meniscus height (TMH), tear film break-up time (TBUT), corneal fluorescein staining (CFS), meibomian gland (MG) function, and tear cytokines. The associations between ocular surface parameters and exposure to particulate matter (PM), ozone (O(3)), nitrogen dioxide (NO(2)), and sulfur dioxide (SO(2)) for 1 day, 1 week, and 1 month before the examination were analyzed in single- and multi-pollutant models adjusted for confounding factors. RESULTS: In the multi-pollutant model, the OSDI score was positively correlated with PM with diameter ≤2.5 μm (PM(2.5)), O(3), and SO(2) exposure [PM(2.5): β (1 week/month) = 0.229 (95% confidence interval (CI): 0.035–0.424)/0.211 (95% CI: 0.160–0.583); O(3): β (1 day/week/month) = 0.403 (95% CI: 0.229–0.523)/0.471 (95% CI: 0.252–0.693)/0.468 (95% CI: 0.215–0.732); SO(2): β (1 day/week) = 0.437 (95% CI: 0.193–0.680)/0.470 (95% CI: 0.040–0.901)]. Tear secretion was negatively correlated with O(3) and NO(2) exposures but positively correlated with PM(2.5) levels. Air pollutants were negatively correlated with TBUT and positively related with CFS score. Besides SO(2), all other pollutants were associated with aggravated MG dysfunction (MG expression, secretion, and loss) and tear cytokines increasement, such as PM(2.5) and interleukin-8 (IL-8) [β (1 day) = 0.016 (95% CI: 0.003–0.029)], PM with diameter ≤10 μm (PM(10)) and IL-6 [β (1 day) = 0.019 (95% CI: 0.006–0.033)], NO(2) and IL-6 [β (1 month) = 0.045 (95% CI: 0.018–0.072)], among others. The effects of air pollutants on DED symptoms/signs, MG functions and tear cytokines peaked within 1 week, 1 month, and 1 day, respectively. CONCLUSION: Increased PM(2.5), O(3), and SO(2) exposures caused ocular discomfort and damage with tear film instability. PM(10) exposure led to tear film instability and ocular injury. PM, O(3), and NO(2) exposures aggravated MG dysfunction and upregulated tear cytokine levels. Therefore, each air pollutant may influence DED via different mechanisms within different time windows.